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EBCS-4
Ethiopian Building Code Standard
DESIGN OF COMPOSITE STEEL AND
CONCRETE STRUCTURES
/
Ministry of Works
&.
Urban Development
Addis Aba.ba., Ethiopia.~661
~!do!lfl3 'eq-eqy S!Ppy lu~wdol~A~a U'EqIfi 'fl !np0.A\.Jo AllS!u!W @
FOREWORD
The Proclamation to define the powers and duties of the Central and Regional Executive Organs of the Transitional Government of Ethiopia No. 41/1993 empowers the Ministry of Works and Urban Development to prepare the Country's Building Code, issue Standards for design and construction works, and follow up and supervise the implementation of same.
In exercise of these powers and in discharge of its responsibility, the Ministry is issuing a series of Building Code Standards of general application.
The purpose of these standards is to serve as nationally recognized documents, the application of which is deemed to ensure compliance of buildings with the minimum requirements tor design, construction and quality of materials set down by the National Building Code.
The major benefits to be gained in applying these standards are the harmonization of professional practice and the ensuring of appropriate levels of safety, health and economy with due consideration of the objective conditions and needs of the country.
As these standards are technical documents which, by their very nature, require periodic updating, revised editions will be issued by the Ministry from time to time as appropriate.
The Ministry welcomes comments and suggestions on all aspect of the Ethiopian Building Code Standards. All feedback received will be carefully reviewed by professional experts in the field of building construction with a view to possible incorporation of amendments in future editions.
Haile Assegidie Minister
Ministry of Works and Urban Development
EBCS·4
Design of Composite steel
and conereee
structures
Project Council Members
Abashawl Woldemariam (Chairman) Almayehu Gizawt Bekele Mekonnen Negussie Tebedge Seifu Birke Wouhib Kebede tDeceased Editor
Prof. Negussie Tebedge \
Technical Committee Members
Negussie Tebedge (Secretary) Delellegne Teshome
Michael Albrecht Yibeltal Zewdie
TABLE OF CONTENTS
CHAPTER 1 - INTRODUCTION 1 1.1 SCOPE 1 1.2 ASSUMPTIONS 1 1.3 UNITS . 1 1.4 SYMBOLS 1CHAPTER 2 -BASIS OF DESIGN 7
2.1 FUNDAMENTAL REQUIREMENTS 2.2 LIMIT STATES
2.2.2 Ultimate Limit States
7 7
8 2.2.3 Serviceability Limit State
2.3 DESIGN SITUATIONS 2.4 ACTIONS
8 8
8
2.4.1 Definitions and Principal Classification 8
2.4.2 Representative Values of Actions 9
2.4.3 Representative Values of Permanent Actions 9
2.4.4 Representative Values of Variable Actions 10
2.4.5 RepresentativeValues of Accidental Actions 10
2.4.6 Design Values of Actions 10
2.4.7 Design Values of the Effect of Actions 11
2.5 MATERIALS 11
2.5.1 Characteristic Strength 11
2.5.2 Design Values 12
2.6 GEOMETRICAL DATA 12
2.7 LOAD ARRANGEMENTS AND LOAD CASES 12
2.8 DESIGN REQUIREMENTS 13
2.8.1 General 13
. 2.8.2 Ultimate Limit States 13
.. 2.8.2.1
Verification Conditions
132.8.2.2 Combinations of Actions
142.8.2.3 Design Values of Permanent Actions
152.8.2.4 Verification of Static Equilibrium
152.8.3 Partial Safety Factors for Ultimate Limit States 16
2.8.3.1 Partial Safety Factors for Actions on Building Structures
16. ,~8.3.2
Partial Safety Factors for Resistances
172.8.4 Serviceability Limit States 17
2.9 DURABILITY 18
CHAPTER 3 - MATERIALS 19
3.1/ CONCRETE 19
3.1.1 General 19
3.1.2 Grades of Concrete 19
3.1.3 Characteristic Compressive Strength of Concrete 19
3.1.4 Characteristic Tensile Strength
20
3.1.5 Deformation Properties of Concrete
20
3.1.5.1
Stress-Strain Diagrams
213.1.5.2
Modulus of Elasticity
213.1.5.3 Modular Ratios 21
3.1.5.4 Poison's Ratio 22
3. 1.5.5 Creep and Shrinkage . 22
3.1.5.6 Coefficient of Thermal Expansion .23
3.2 REINFORCING STEEL ·23
3.2.1 Characteristic Strength of Reinforcing Steel 23
3.2.2 Classification and Geometry of Reinforcing Steel 23
3.2.3 Physical Properties of Reinforcing Steel 24
3.2.4 Mechanical Properties of Reinforcing Steel . 24
3.2.4.1 Strength 24
3.2.4.2 Ductility . 24
3.2.4.4 Modulus of Elasticity 25
3.2.4.5 Fatigue 25
3.2.5 Technological Properties 25
3.2.5.1 Bond and Anchorage 25
3.2.5.2 Weldability 25
3.3 STRUCTURAL STEEL 25
3.3.1 Scope 25
3.3.2 Material Properties for Hot Rolled Steel 26
3.3.2.1 Nominal Values 26
3.3.2.2 Plastic Analysis 26
3.3.2.3 Fracture Toughness 27
3.3.3 Dimensions, Mass' and Tolerances 27
3.3.4 Design values of Material Coefficients 27
3.4 CONNECTING DEVICES 27
3.4.1 General 27
3.4.2 Shear Connection 27
CHAPTER 4 - ULTIMATE LIMIT STATES 29
4.1 BASIS 29
4.1:1 General 30
4.1.2 Beams 31
4.1.3 Composite Columns and Connections 31
4.2 PROPERTIES OF CROSS-SECTIONS OF BEAMS 31
4.2.1 Effective Section 31
4.2.2 Effective Width of Concrete Flange for Beams in Buildings 32
4.2.2.1. Effective Widthfor GlobalAnalysis 32
4.2.2.2 Effective Widthfor Verification of Cross-sections 33
4.2.3 Flexural Stiffness 33
4.3 CLASSIFICATION OF CROSS-SECTIONS OF BEAMS 33
4.3.1 General 33
4.3.2 Classification of Steel Flanges in Compression 34
4.3.3 Classification of Steel Webs ·34
4.3.3.1 Section Where the Compression Flange is in Class 1 or 2 35
4.4 RESISTANCES OF CROSS-SECTIONS OF BEAMS 35
4.4.1 Bending Moment . 35
4.4.1.1 Basis 35
4.4.1.2 Plastic Resistance Moment of a Section with Full Shear Connection 35
4.4 .1.3 Plastic Resistance Moment of a Section with Partial Shear Connection 38
4.4.1.4 Elastic Resistance to Bending 38
4.4.2 Vertical Shear 39
4,4.2.1 Scope 39
4.4.2.2 Design Methods· 39
4.4.3 Bending and Vertical Shear 40
4.4.4 Shear Buckling Resistance 40
4.4.5 Interaction Between Bending.and Shear Buckling 42 .
4.5 INTERNAL FORCES AND MOMENTS IN CONTINUOUS BEAMS 42
4.5.1 General 42 4.5.2 Plastic Analysis 42 4.5.2.1 General 42 4.5.2.2 Requirementsfor Rigid-PlasticAnalysis 42 4.5.3 Elastic Analysis 43 4.5.3.1 General 43 4.5.3.2 Sequence of Construction 43 .
4.5.3.3 Effects of Shrinkage of Concrete in Beamsfor Buildings 43
4.5.3.4 Redistribution of Moments in Beamsfor Buildings 43
4.6 LATERAL-TORSIONAL BUCKLING OF COMPOSITE BEAMS FOR BUILDINGS 44
4.6.1 General 44
4.6.2 Check without Direct Calculation 46
4.6.3 Buckling Resistance Moment 47
4.6.4 Simplified Method of Calculation of the Slenderness Ratio and the Elastic Critical
Momem 47
4.6.4.1 Slenderness Ratio 47
4.6.4.2 Elastic Critical Moments 47
4.6.4.3 Double Symmetrical Steel Sections 49
4.6.4.4 Mono-Symmetrical Steel Sections 48
4.6.4.5 Alternative Methods of Calculation 50
4.7 WEB CRIPPLING 50
4.7.1 General 50
4.7.2 Effective Web in Class 2 50
4.8 COMPOSITE COLUMNS 53
4.8.1 Scope 53 .
4.8.2 General Method of Design 54
4.8.2.1 General 54
4.8.2.2 Design Procedures 54
4.8.2.3 Imperfections 54
4.8.2.4 Local Buckling of Steel Members 55
4.8.2.5 Cover and Reinforcement 56
4.8.2.6 Shear Between the Steel and Concrete Components 57
4~8.2. 7 Resistance to Shear 57
4.8.2.8 Stud Connectors Attached to the Web of a Composite Column 57
4.8.3 Simplified Method of Design 58
4.8.3.1 Scope 58
4.8.3.2 Partial Safety Factors 'YMa' "la' and 'YRd 59
4.8.3.3 Resistance of Cross Sections to Axial Loads 60
4.8.3.4 Steel Contribution Ratio 61
4.8.3.5 Effective Elastic Flexural Stiffness of Cross Sections 61
4.8.3.6 Buckling Length of a Column 62
4.8.3.7 Relative Slenderness 62
4.8.3.8 Resistance of Members in Axial Compression 63
4.8.3.9 Combined Compression and Bending 63
4.8.3.10 Analysis for Bending Moments 63
4.8.3.11 .Resistance of Cross Sections in Combined Compression and Uniaxial
Bending 64
4.8.3 .12 Influence of Shear Forces 65
4.8.3.,13 Resistance of Members in Combined Compression and Uniaxial Bending 65
4.8.3.14 Combined Compression and Biaxial Bending 68
4.804.Design of Composite Col1J11111S with Mono-Symmetrical Cross Sections - Simplified
Method . 69 '
4.8.4.1 General 69
4.8.4.2 Scope. 69
.4.8.4.3 Design for Axial Compression 69
4.8.4.4· Designfor Compression and Uniaxial Bending 69
. 4.8.4.5 Long-Term Behaviour of Concrete 70
Simplified Calculation Method for Resistance of Doubly Symmetric
Composite Cross Sections in Combined Compression and Bending 71 4.8.5
4~8.5.1Scope and Assumptions . 71
4.8.5.2 Compressive Resistances 71
4.8.5.3 Position of Neutral Axis 72
4.8.5.4 Bending Resistances 72
.4.8.5.5 Interaction with Transverse Shear 73
4.8.6 Neutral Axes and Plastic Section Moduli of Some Cross Sections 73
4.8.6.1 General 73
4.8.6.2 Major Axis Bending of Encased I-sections 74
4.8.6.3 Minor Axis Bending of Encased I-sections 75
·4.8.6,4 Concrete Filled Circular and Rectangular Hollow Sections
76
4.9 INTERNAL FORCES AND MOMENTS IN FRAMES FOR BUILDINGS 78
4.9.1 General 78 4.9.2 Design Assumptions 78 4.9.2.1 Basis 78 4.9.2.2 Simple Framing 79 4.9.2.3 Continuous Framing 79 4.9.2.4 Semi-Continuous Framing 79 4.9.2.5 Effects of Deformations 79
4.9.3 Allowance for Imperfections
80
4.9.4 Sway Resistance
80
4.9.4; 1 General
80
4.9.4.2 Classification as Sway or Nun-Sway
80
4.9.4.3 Classification as Braced or Unbraced
80
4.9.5 Methods of Global Analysis .
80
4.9.6 Elastic Global Analysis 81
4.9.6.1 General 81
4.9.6.2 Flexural Stiffness 81
4.9.6.3 Redistribution of Moments 81
4.9.7 Rigid-Plastic Global Analysis 82
4.9.7.1 General 82
4.9.7.2· Plastic Hinges ·82
. 4.10 COMPOSITE CONNECTIONS IN BRACED FRAMES FOR BUILDINGS 83
4.10.1 General 83
4.10.2 Classification of Connections 83
4.10.3 Connections Made-with Bolts, Rivets or Pins 84
4.10.3.1 General 84
4.10.3.2 Distribution of Forces Between Fasteners 84
4.10.3.3 Pin Connections 84
4.10,4 Splices in Composite Members 84
4.10.5 Beam-to-Column Coimections 84
4_105.1 General 84
4.10.5.2 Classification by Rotational Stiffness 84
4.10.5.3 Classification by Moment Resistance 84
4.10.5.4 Classification of Moment-Rotation Characteristics 84
.4.10.55 Calculated Properties 85
4.10.5.6 Application Rules 85
CHAPTER 5 - SERVICEABILITY LIMIT STATES 87
5.1 GENERAL. 87
5.2 DEFORMATIONS 'y 87
5.2.1 General 87
·5.2.2 Calculation of Maximum Deflections of Beams 88
5.3 CRACKING OF CONCRETE IN BEAMS 89
5.3.1 General 89
5.3.2 Minimum Reinforcement 91
5
.s.s
Analysis of the Structure for the Control of Cracking . . 925.3.4 Control of Cracking due to Direct Loading without Calculation of Crack Widths 92 5.3
5.
Control of Cracking by Calculation of Crack Widths 93CHAPTER 6 - SHEAR CONNECTION IN BEAMS FOR BUILDINGS 9S
6.1 GENERAL 95
6.1.1 Basis of Design 95
.6.1.2 Deformation Capacity of Shear Connectors 95
6.1.3 Spacing of Shear Connectors 97
6.2. LONGITUDINAL SHEAR FORCE 97
. 6.2.1 Beams in which Plastic Theory is Used for Resistance of Cross-Section 97
6.2.1.1 Full Shear Connection 97
6.2.1.2 Partial Shear Connection with Ductile Connectors 98
6.2.1.3 Partial Shear Connection with Non-Ductile Connectors 100
·6.2.2 Beams in which Elastic Theory is used for Resistances of One or More Cross
Sections 101
6.3 DESIGN RESISTANCE OF SHEAR CONNECTORS 101
6.3.1 General 101
·6.3.2 Stud Connectors in Solid Slabs 101
6.3.2.1 Headed Studs - Shear Resistance 101
·6.3.2.2 Influence of Tension on Shear Resistance 102
6.3.2.3 Studs Without Head - Shear Resistance 102
6.3.3 Headed Studs Used with Profiled Steel Sheeting 102
.. 6.3.3.1 Sheeting with Ribs Parallel to the Supporting Beams 102
6.3.3.2 Sheeting with Ribs Transverse to the Supporting Beams 103
6.3.3.3 Biaxial Loading of Shear Connectors 103
6.3.4 Block Connectors in Solid Slabs 104
6.3.5 Anchors and Hoops in solid Slabs 105
·6.3.6 Block Connectors with Anchors or Hoops in Solid Slabs 107
6.3.7 Angle Connectors in Solid Slabs 107
6.4 DETAILING OF THE SHEAR CONNECTION 108
6.4.1 General Recommendations 108
6.4.1.1 Resistanceto Separation 108
. 6.4.1.2 Coverand Compaction of Concrete 108
6.4.1.3 Local Reinforcement in the Slab 108
. 6.4.1.4 Haunches Other than Formed by Profiled Steel Sheeting 109
6.4~ 1.5 Spacing of Connectors 110
6.4.1.6 Dimensions of the Steel Flange· 110
6.4.2 Stud Connectors
110
6.4.3 HeadedStuds Used with Profiled Steel Sheeting
110
6.4.3.1 General
110
6.4.3.2 Sheeting with Ribs Transverse to the Supporting Beams
110'
6.4.4 Block Connectors
'
111
6.4.5 Anchors
and-Hoops
111
6.4.6 Angle Connectors
111
. 6;5
FRICT~ONGRIP BOLTS
112
6.5.1 General
,
112
6.5.2 Ultimate Limit State
112
6.5.2.1 Design Friction Resistance
112
. (i.5.2:2
Design Resistance ola Bolt in Shear
and
Bearing
112
6.5.2.3 Combined Resistanc«
112
6.5.2.4 Effects
0/
SUp
112
6.5.3 Serviceability Limit State
113
6.6 TRANSVERSE REINFORCEMENT
113
6.6.1 Longitudinal Shear inthe Slab
113
6.6.2 DesignResistance'to Longitudinal Shear
114
6.6.3 Contribution of Profiled Steel Sheeting.
U5
6.6.4 Minimum Transverse.Reintorcement
116
6.6.4.1 Solid Slabs
116
6.6.4.2 Ribbed Slabs
116
6.6,5 Longitudinal Splitting
116
CHAPTER 7 • FLOORS WITH PRECAST CONCRETE SLABS FOR BUILDINGS 117
7.1 GENERAL
,117
7.2 ACTIONS
117
7.3 PARTIAL SAFETY FACTORS FOR MATERIALS
117
7.4 DESIGN, ANALYSIS, AND DETAILING OF THE FLOOR SYSTEM
117
7.4.1.
Support Arrangements
117
7.4.2.Joints Between Precast Elements
117
7.4.3 Interfaces
118
7.5 JOINT BETWEEN STEEL BEAMS AND
CO~CRETESLAB
118
7.5.1 Bedding and Tolerances
118
7.5.2 Corrosion
118
7.5.3 Shear Connection and Transverse Reinforcement ,
118
7.6 CONCRETE FLOOR DESIGNED FOR HORIZONTAL LOADING
119
CHAPTER 8 • EXECUTION
121
8.1 GENERAL
121
8.2 SEQUENCE OF CONSTRUCTION
121
8.3 STABILITY
121
8.4 ACCURACY OURINO CONSTRUCTION AND QUALITY CONTROL
121
8.4.1 Static Deflection During and After Concreting
121
8.4.2 Compaction of Concrete
, . 122
8.4.3 Shear Connection in Beams and Columns
122
8.4.3.1 Headed, Studs in Structures/or Buildings
122
, 8.4.3.2
Anchors, Hoops, Block Connectors
122
8.4;3.3 Friction Grip Bolts
122
8.4.3.4 Corrosion Protection in the Interface
122
CHAPTER
1
INTRODUCTION
1.1
,SCOPE
(1) This Ethiopian Buildins Code Standard EBCS
4"Design of Composite Steel and Concrete
Structures" applies to the design of composite structures and members for buildings rand civil .
enalnoerlna works. The composite structures andmeinbers are made of structural steel and,teinforced
or prestressed concrete
connected
together to resist loads.
(
(2) Thla ,Code 11 orily concerned withthe requirements for resistance, serviceability and durability of
struotur.a, Other requirements,
e.g,concerning thermal or sound insulation are not considered.
(3) Ex.ecutlon 11 covered in Chapter 8, and by reference to EBCS 2 and EBCS
3 to the extent that itis
noel.
air)' to Indicate the quality of the construction materials and products which should be used
and
the
atandard
of
worlananship on site needed to comply with the assumptions of the design rules.
Generall)'
Ithe rules related to execution and workmanship are to be
considered asminimum
requirements which may have to be further developed for particular types of buildings or civil
. - enalnolrll1l workl and methods of construction.
(4) Thl' Codl does not cover the special requirements of seismic design: Provisions related to such
, requlromenta
are
provided in EBCS 8 "Design of Structures for Earthquake Resistance" which
complements or adapts the rules of BBCS 4 specifically for this purpose.
(5) N~.rloal
values of the actions on buildings and, civilengineering works to be taken intoaccount '
In thl d,.lln are not given in BBCS
4.They are given in EBCS
1 -Basis of " Design and Actions
on Struotures" applicable to the various types of construction.
1.2
ASSUMP110NS
(1) The ..aumptlons given in BBCS 2 and BBCS 3 are applicable.
(2) Thedl.lln procedures are valid only when therequirements for execution andworkmanship given
in Chapter
8
are also complied, with.
1.3
lJNITS
(1) S,l, Units shall be used in accordance with ISO 1000. (2) Par oaloulatlons,. the following units are recommended:
(a) forces
and loads
kN,kN/m, kN/m2kg/m' .
(b)
units mass
(c) unit weight
kN/ril3(d) stresses
andstrengths
MPa, OPa'(MN/m2, N/mm2, kN/rnm2)
(e) moments
kNm.ETHIOPIAN BUILDING CODE STANDARD FOR DESIGN OF COMPOSITE STEEL AND CONCRETE STRUCTURES
1.4 SYMBOLS
(1) The symbols used in this Code are as follows:
A . Accident action
Area of the equivalent composite section
A.. The area of the structural steel section
Ac Effective area of concrete
ACI' Mean cross sectional area per unit length of beam of the concrete shear surface under consideration
Ad Design value (specified value) of the accidental actions
At Cross sectional area of reinforcement bar
A't Sum of the cross sectional areas of transverse reinforcement (assumed to be' perpendicular to the beam) per unit length of beam crossing the shear surface under consideration including any reinforcement provided for bending of the slab
A.fl Area of the front surface of a block connector .
All Area of the front surface of a block connector enlarged at a slope of 1:5 to the rear
surface of the adjacent connector .
Ah Cross sectional area of the anchor or the hoop
A p Cross sectional area of the profiled steel sheeting per unit length of the beam
As Effective area of longitudinal slab reinforcement
Ast Area of any longitudinal reinforcement in compression that is included in the calculation of the bending resistance
Am The sum of the areas of the reinforcing bars within the depth of 2hn
Ami The areas of reinforcing bars within 2hn
a Area of structural steel Area of the structural steel
Center to center spacing between the steel beams
ad Geometrical design value
b Breadth of the top flange of the steel member Length of an angle connector
Width of flange of the steel member
bc Breadth of concrete
Cd Design capacity for the effect of actions
e p . . .Factor based on the property of the bending moment within the length L
D, Damage indication
d Diameter of the studs
E.. Modulus of elasticity for steel
E';
Effective modulus' of concrete'for long term effectsEcm Secant modulus of concrete
Ecm Mean value of the secant modulus of the concrete
Ed Design value of the particular effect of actions being considered
Ea1Es Elastic moduli for the structural steel and the reinforcement
Ed,dst Design effect of the destabilizing actions
Ed,stb Design effect of the stabilizing actions'
Ei Stiffness moduli for the relevant areas
CHAPTER 1: INTRODUCTION e ees e, eel eel,l ezj Fe Fd FeQ
s,
F
Q Fse, FIe:
Jek.Ii
Js».fckIsk
I~.. s. .
/y
/YdJlsdJJ
aJ/yp
G GG
dG
ind . G k G1cJ h hehE
hn ho hs 1",lc'Is liifr. lat lay,/azEccentricity of the loading
Additional eccentricity of the permanent normal force
Distance of the reinforcement bars to the relevance middle line ·Elastic centroidal axis for short term loading
Elastic centroidal axis for long tetm loading Distance from the middle line
Compressive force in the concrete flange necessary to resist the design sagging bending Moment M&/, calculated from plastic theory
Design value
Compressive force in the concrete slab at moment MeQ,Rd
Characteristic values
Design longitudinal force caused by composite action in the beam Service values
. Design transverse force caused by composite action in the slab Design tensile force per stud
Characteristic compressive strength of concrete Design strengths of the materials for the areas
Characteristic strengths for the reinforcement and the concrete Characteristic tensile yield strength of reinforcement
Tensile strength of the studs
Specified ultimate tensile strength of the material of a stud, a bolt, a rivet Nominal tensile yield strength of structural steel
Yield strength 'of the structural steel
Design strengths for the structural steel, the reinforcement, and the concrete Characteristic (nominal) tensile yield strength of profiled steel sheeting
Shear modulus for steel Permanent action
Design permanent action Indirect permanent action Characteristic permanent action
Characteristic values of the permanent actions
·Greater overall dimension of the section parallel to a principal axis
Height of the upstanding leg of an angle connector overall height of the stud Height of column or storey height
Overall depth of the steel member Depth of concrete
"Depth to the additional point E
Depth of the neutral axis in the web Overall height of structure
Distance center to center of flanges
Distance between the shear center of the flanges of the. steel member Distance to the neutral axis
Second moments of area for the considered bending plane of the structural steel, the concrete (assumed to be uncracked) and the reinforcement, respectively
·Second moment of area of the bottom flange about the minor axis of the steel member St. Venant torsion constant 0 the steel section
Second moment of area of the structural steel section about its center of area, C
ETHIOPIAN BUILDING CODE STANDARD FOR DESIGN OF COMPOSitE STEEL AND CONCRETE STRUCTURES
t,
Second moment of area for major axis bendingi
Radius of gyrationk Correlation factor
kc Factor'
ks Transverse stiffness per unit length of beam
k1 Flexural stiffness of cracked concrete or composite slab, in the direction transverse
to the steel beam
k,. Flexural stiffness of the steel web
L
Length of the beam between points at which the bottom flange of the steel member in laterally restrainedSpan of the composite structure System length
I Buckling length
Mopl,Rd Design plastic resistance to bending of the structural steel section alone
, Ma;Sd Moment acting in the steel section due to actions on the structural steelwork alone before the composite action becomes effective ' ' Design buckling resistant moment of a laterally unrestrained beam
Mb,Rd
Elastic critical moment for lateral-torsional buckling
Mcr
ME,Rd Resistance moment at the additional point E
Value of M,I,Rd when the 'Yilt factors 'YOI.'YC' andlY, are taken as unity
M"
M,I,Rd Elastic resistance to bending
M,Q.Rd Moment that causes a stressf/'Ya in the extreme bottom fibre of the steel section
u;
Value of Mpl,Rd when the 'Ym factors 'Y..."Vc• and "V, are taken as unityPlastic resistance moment Mpl,Rd
Mpl,Rd Plastic design value of the resisting bending moment Mpl,y,Rtl,Mpl,r.Rd, Plastic resistance moment about the major and minor axis
Compressive resistance force for the whole area of the' concrete Npm,Rd
MIflIlZ,Sd Greatest design moment calculated by first order theory Design value of the applied internal bending moment
M
SdGreatest first order design bendingmoment
Design bending moments about the major and minor axis M"JlbMr.sd
N Number of connectors provided within the same length of beam
»;
Elastic critical loadNcr Critical load for the relevant axis
NE,ME Normal force and bending moment at the additional point
E
NE,Rd Resistance force at the additional point ENJ Number of shear connectors determined for the relevant length of beam Plastic resistance to compression
Npl'Rd
Plastic resistance load for the concrete section alone
N
w Design axial forcen
Modular ratioNpm,Rd
Cross sectional area of the profiled steel sheeting per unit length of the beam
P
Design bearing resistance of a headed stud welded through the sheet Ppb,Rd
PRd Design shear resistance of a composite structure connector
Q Variable action
CHAPTER 1: INTRODUt?.Tl0!t
---~---...;.----Q
Variable action
Qd
Design variable action
Qilld
Indirect variable action
QJ;
Characteristic variable action
Qk,/
Characteristic values of the other variable actions
Qk,'
Characteristic value of one of the variable actions
Rd
Design resistance of material property
RJ;
Characteristic resistance of material property
r
Ratio or the lesser to the greater end moment
54
Design value of internal force or
moment
58
Sum of the areas of reinforcement lying in the additional compressed region
S
Effective area of longitudinal slab reinforcement
Longitudinal spacing of studs or rows of studs
Steel contribution ratio
The longitudinal spacing of studs or rows of studs
s,
Areaof any longitudinal reinforcement in compression that is included in the calcula
tion of the bending resistance
.
Centre-to-centre spacing of shear connectors in the direction of compression
'1
Distance from the edge of a compression flange to the nearest line of connectors
'2
t
Thickness of the flange
t
Thickness of the wall of a concrete-filled hollow section
t,
Thickness of flange
t'AI
Thickness of web of the steel member
Total design longitudinal shear
~
Design transverse shear force
VSd
Design resistance to longitudinal shear
v
RtlVSd
Design longitudinal shear per unit length
WpaPlastic section modulus for the structural steel
Wpc
Plastic section modulus for the concrete
Wps
Plastic section modulus of the total reinforcement
W]HIII1 Wp.w WPeR . Plastic
section moduli for the structural steel, the reinforcement and the concrete
parts of the section
x,
Design value of material property
iXJ;
Characteristic value of material property
%c
Distance between the center of area of the steel member and mid-depth of the slab
Distances to the reference axis for the calculation
%/
a
Coefficient of linear thermal' expansion
Angle between the anchor bar or the hoop and the plane of the flanges of the beam'
p
Angle in the horizontal plane between the anchor bar and the longitudinal axis of the
.beam for anchors set at a splay
Factor for the determination of. moments according to second-order msonary
Equivalent moment factor
ETHIOPIAN BUILDING CODE STANDARD FOR DESIGN OF COMPOSITE STEEL AND CONCRETE STRUCTURES
'YG.j Partial safety factor for the permanent action Gk.j
'YGA.j As 'YGJ but for accidental design situations
'YQ.i Partial safety factor for the variable action QK.i
''If;''YQ1 'Yo Partial safety factors
iii,
'YS Partial safety factors for structural steel and reinforcement'Yc Partial safety factor for concrete
'Yap Partial safety factor fer profiled steel sheeting
°PllilX
00
Sagging in the final state relative to the straight line joining the supports. Pre-camber(hogging) of the beam in the unloaded state, (state 0). . .
01 Variation of the deflection of the beam due to the permanent loads immediately after loading, (state 1).
02 Variation of the deflection of the beam due to the variable loading plus any time dependent deformations due to the permanent load, (stale 2) .
A
Relative stiffnessA
Relevant slendernessAl.T Slenderness ratio for lateral-torsional buckling
P-d Bending resistance of the cross section
P-lc Characteristic value of he bending moment of the cross section
P Poison's ratio
Po Poison's ratio for steel
Ppd Contribution of the steel sheeting
p Unit mass
TRd Basic shear strength
XLT Reduction factor for lateral-torsional buckling
X Reduction coefficient for the relevant buckling mode
x
Factor taking account for the influence of imperfection and slenderness 1/;0,1/;1' 1/;2 Load factorsEBCS 4_ 1995
CHAPTER
,2
BASIS OF DESIGN
2.1 FUNDAMENTAL REQUIREMENTS
(1) A structure shall be designed and constructed in such a way that:
(a) With acceptable probability, it will remain fit for the use for which it is required, having due regard to its intended life and its cost, and
(b) with appropriate degrees of reliability, it will sustain all actions and other influences likely to occur during execution and use and have adequate durability in relation to maintenance costs.
(2) A structure shall also be designed in such a way that it will not be damaged by events like explosions, impact or consequences of human errors, to an extent disproportionate to the .original cause.
(3) The potential damage should be limited or avoided by appropriate choice of one or more of the , following:
(a) Avoiding, eliminating or reducing he hazards which the structure is to sustain (b) Selecting a structural form which has low sensitivity to the hazards considered
(c) Selecting a structural form and design that can survive adequately the accidental removal of an individual element
.Id) Tying the structure together
(4) The above requirements shall be met by the choice of suitable materials, by appropriate design and detailing and by specifying control procedures for production, construction and use as relevant for/the particular project.
/
2.2 LIMIT STATES 2.2.1 General
(1) A structure, or part of a structure, is considered unfit for use when it exceeds a particular state, called a limit state, beyond which it infringes one of the criteria governing its performance or use.
(2) All relevant limit states shall be considered in the design so as to ensure an adequate degree of safety and serviceability. The usual approach will be to design on the basis of the most critical limit state and then to check that the remaining limit states will not be reached. I
. (f) TIJe limit states can be placed in two categories:
(a) The Ultimate Limit' States are those associated with collapse, or with other forms of
structural failure which may endanger the safety of people. States prior to structural collapse which, for simplicity, are considered in place of the collapse itself are also treated as ultimate limit states.
(b) The Serviceability Limit States correspond to states beyond which specified service
requirements are no 'longer met.
ETHIOPIAN BUILDING CODE STANDARD FOR DESIGN OF COMPOSITE STEEL AND CONCRETE STRUCTURES
2.2.2 Ultimate l-imit States
(1) The ultimate limit states which may require consideration include:I . .
(a) Loss of equilibrium of a part or the whole of the structure considered as a rigid body. (b) Failure by excessivedeformation, rupture or loss of stability of the structure or any part of
it, including supports and foundations.
(2) Limit states may also concern only concrete or steel parts of the structure (e.g. the steel part during an erection phase), for which reference should be made to EBCS 2 and EBCS 3, respectively.
2.2.3 serviceability Limit ~~ate
(1) Serviceability limit .states which may require consideration include:
(a) Deformations or deflections which affect the appearance or effective use of the structure (including the malfunction of machines or services) or cause damage to finishes of non"; structural elements.
(b) Vibration which causes discomfort to people, damage to the building or its contents, or which
limits its functional effectiveness. ' ,
(c) Cracking of the concrete which is likely to affect appearance, durability or water-lightness
adversely. ;
(d) Damage to concrete because of excessive compression, which is likely to lead to loss of
durability. '
(e) Slip at the steel-concrete interface when it becomes large enough to invalidate design checks for other, serviceability limit states in which the effects of slip are neglected.
2.3 DESIGN SITUATIONS
(1) Design situations are classified' as:
(a) Persistent situations corresponding to normal conditions of use of the structure. (b) Transient situations, for example during construction or repair.
(c) Accidental situations.
(2) For composite structures attention is drawn to the necessity of identifying and considering, when .relevant, several transient design situations corresponding to the successive phases of the building process. For example, it may be necessary not only to consider the situation of the steel beam supporting the fresh concrete, but even to distinguish several situations corresponding to successive phases of pouring the concrete."
2.4 ACTIONS
2.4.1 Deflnitlons and Princi~ Classification (1) An action F is:
(a) a force (load) applied to the structure (direct action), or
(b) an imposed deformation (indirect action); for example, temperature effects or settlement.
CHAPT£R 2: BASIS OF DESIGN
(2) Actions are classified:
(a) By their variation in time:. . '
(i) Permanent actions (G), e.g, self-weight of structures, fittings, ancillaries and fixed equipment.
(ii), Variable actions (Q), e.g. imposed loads or wind loads.
(iii). Accidental actions (A), e.g. explosions or impact from vehicles.
(b) By their spatial variation:
(i) Fixed actions, e.g. self-weight.
. (ii) Free actions, which result In different arrangements of actions, e.g. movable imposed loads and wind loads, .
(~) Indirect actions are either permanent G'M (e.g. settlement of support) or variable Q;nd (e.g. temperature) and are treated accordingly .
. (4) Supplementary classifications relating to the response of the structure are given in the relevant clauses.
2.4.2 Representative Values of Actjons
(1) For verification in the partial safety coefficient.method, actions are introduced, into the calculations by representative values, i.e. by values corresponding to certain levels of intensity. For different calculations, one may have to distinguish different
representative
values of an action, according to its variation in time. The complete set of representative values is as follows:(a) Characteristic values; Pk
(b) Service values; Fser (c) Combination values;VtOFk (d) Frequent values;
VttFk
(e) Quasi-permanent values:
VtzF"
-,
The factors Vt; are defined in Section 2.4.4(5). The above valves are evaluated mainly on a statistical basis.
(2) Maximu,m values and minimum values, which may be zero, are defined when appropriate.
<,
(3) Depending on the variation with time of certain actions, their representative values are sometimes subclassified as actions of long durat~n (or sustained actions) or of short duration (or transient actions). In special cases, certain actions have their representative values divided into sustained and transient components.
2.4.3 Representative Values of Permanent Actions
(1) The representative values of permanent actions are specified as:
(a) The characteristic values Fk specified in EBCS 1 - "Basis of Design and Actions on
Structures", or
(b) by the client, or the' designer in consultation with the client, provided that minimum provisions, specified in the relevant codes or by the competent authority, are observed.
(2) The other representative values are assumed to be equal to those in (1) above.
ETHIOPIAN BUILDING CODE STANDARD FOR DESIGN OF COMPOSITE STEEL AND CONCRETE STRUCTURES
(3) For permanent actions where the coefficient of variation is large or where the actions are likely to vary during the life of the structure (e.g. for some superimposed permanent loads), two characteristic values are distinguished, an upper (Gk,sup) and a lower (Gk,;nf)' Elsewhere a single characteristic value (GTe> is sufficient.
(4) The self-weight of the structure may, in most cases, be calculated on the basis of the nominal dimensions and mean unit masses.
2.4.4 Representative Values of Variable Actions
(1) The main representative value is the characteristic value Qk'
(2) For variable actions the characteristic value Qk corresponds to either:
(a) The upper value with an intended probability of not being exceeded or the lower value with an intended probability of not being reached, during some reference period, having regard to the intended life of the structure or the aSSUIIlt:u duration of the design situation,or (b) the specified value.
(3) Other representative values are expressed in terms of the characteristic value (1 by means of a factor 1/1;. These values are defined as:
(a) Combination value: 1/IOQk (b) Frequent value: 1/IIQk
(c) Quasi-permanent value: 1/I2Qk
(4) Supplementary representative values are used for fatigue verification and dynamic analysis.
(5) The factors 1/1; are specified:
(a) In EBCS 1 - "Basis of Design and Actions on Structures", or
(b) by the client or the designer in conjunction with .the client, provided that mimmum provisions, specified in the relevant codes or by the competent public authority, are observed.
2.4.5 Representative Values of Accidental Actions
(1) The representative value of accidental actions is the characteristic value Ak (when relevant) and generally correspond to a specified unique nominal value beyond which there is no longer an assurance of a probability of survival of the structure.
(2) Their service, combination and frequent values are considered negligible or zero.
2.4.6 Design Values of Actions
(1) The design value Fd of an action is expressed in general terms as
r,
=
'Y~k(2.1)
CHAPTER 2: BASIS OF DESIGN
Specific examples are:
G,
=
'YGGkQd= 'YQQk or 'YQWjQk
Ad
=
.y~k (if Ad is not directly specified)P,
=
'Ypl'k (2.2)where 'YF> 'YG' 'YQ' 'YA and Y» are the partial safety factors for the action considered taking account of. for example, the possibility of unfavourable deviations of the actions, the possibility of inaccurate modelling of the actions, uncertainties in the assessment of effects of actions, and uncertainties in the assessmentof the limit state considered.
(2) The upper and lower design values of permanent acrions are expressed as follows:
(a) Where only a single characteristic value G, is used, then
Gd,sup
=
'YG,sup GkGd,jn[
=
'YG,jnf G k(b) Where upper and lower cfiaracteristic values of permanent actions are used, then
Gd.sup -- 'Y G,sup Gk.sup
Gd,in[
=
'YG,inf Gk,infwhere Gk,jn[ is the lower characteristic value of the permanent action
«;
is the upper characteristic value of the permanent action'YG,in[ is the lower value of the partial safety factor for the permanent action
is the lower value of the partial safety factor for the permanent action
'YG,sUP
2.4.7 Design Values of the Effect of Actions
(1) The effects of actions are responses (e.g. internal forces and moments, stresses, strains) of the structure to the actions. Design values of the effects of actions are determined from the design values of the actions, geometrical data and material properties when relevant.
(2) In some cases, in particular for nonlinear analysis, the effect of the randomness of the intensity of the actions and the uncertainty associated with the analytical procedures, e.g. the models used in the calculations, should be considered separately. This may be achieved by the application of a coefficient of model uncertainty, either applied to the actionsor to he internal forces and moments.
2.5 MATERIALS
2.5.1 Characteristic Strength
(1) A material property is represented by a characteristic value which in general corresponds to a fractile in the assumed statistical distribution of the particular property of the material, specified by relevant standards and tested under specified conditions.
""-,
(2) In certain cases a nominal value is used as the characteristic value.
(3) Material properties for steel structures are generally represented by nominal values used as characteristic values.
ETHIOPIAN BUILDING
~'oDE
STANDARD FOR DESIGN OF COMPOSITE STEEL AND CONCRETE STRUCTURES.'
(4) A material property may have two characteristic values, the upper value and the lower value. In
most casesonly the lower values need to be considered. However, the upper values of the ,yield'
strength, for example,
shouldbe considered in special cases where overstrength effects may producea reduction in safety; this is for example the case for the tensile strength of concrete in the calculation
of the effects of indirect actions.
2.5.2 Design Values
(1)
The design value X
dof a material property is generally defined
as:
. , I
X I'
X - k
(2.3)
d -
'YM
where
'YMis the partial safety factor for the material property.
(2) For composite steel and concrete structures, the design resistance
~is generally determined
directly from the characteristic values of the material properties and geometrical data:
R
=
Rk (2.4)d 'YM
where
'YMis the partial safety
factorfor the resistance as provided in EBCS-2 and EBCS-3. (3)The design value
R
dmay be determined from tests.
2.6 GEOMETRICAL DATA
(1)
Geometrical data are generally represented by their nominal values:
ad = anom
(2.5)
(2) In some cases the geometrical design values are defined by:
ad =. allOm
+
sa(2.6)
where
4/1is the additive partial safety margin for geometrical data. The values of
4/1are given in
the appropriate sections.
(3)
For imperfections to be adopted
inthe global analysis of the structure, see Sections 4.8.2.3 and
4.9.3.
2.7 LOAD ARRANGEMENTS AND LOAD CASES
(1) A load arrangement Identifiesthe position, magnitude and direction of a free action.
(2) A load case identifies compatible load arrangements, sets of deformations and imperfections
considered for a particular verification.
(3) For the relevant combinations of actions, sufficient load cases shall be considered to enable the
critical design conditions to be established.
. CHAPTER 2: BASIS OF DESIGN
(4) Simplified load cases may be used, if based on a reasonable interpretation of the structural response.
(5) For continuous beams and slabs in buildings without cantilevers subjected to dominantly uniformly distributed loads, it
will
generally be sufficient to consider only the following load arrangements:(a) Alternate spans carrying the design variable and permanent loads ("Ya Qk
+
"YoOJ,
other spans carrying only the design permanent load "Yo Gk, .(b) Any two adjacent spans carrying the design variable and permanent loads ("YaQk
+
"Yo GJ, all other spans carrying only the design permanent load "Yo Gk•2.8
DESIGN REQUIREMENTS
·2:8.1
General(1).It shall be verified that no relevant limit state is exceeded.
(2) All relevant design situations and load cases shall be considered.
(3)· Possible deviations from the assumed directions or positions
df
actions shall be considered. (4) Calculations shall be performed using appropriate design models (Supplemented, if necessary, by . tests) involving all relevant variables. the models shall be sufficiently precise to predict the structural · behaviour, commensurate with the standard of workmanship likely to be achieved, and with thereliability of the information on which the design is based.
2.8.2 .. Ultimate Limit States
2.8.2.1 Verification Conditions
(1) When considering a limit state of static equilibrium or of gross displacements or deformations of .the structure, it shall be verified that:
Ed,dst
s
Ed,SIb (2.7)where Ed,dst is the design effect of the destabilizing actions
Ed, sib is the design effect of the stabilizing actions.
·.(2)·When considering a lintit state of rupture or excessive deformation of a section, member or .. ·connection (fatigue excluded) it shall be verified that:
s,
S Rd (2.8).where Sd is the design value of an internal force or moment (or of a respective vector of several 'internal forces or moments)
R,
isthecorresponding design resistance, each taking account of the respective design values of all structural properties.(3) When considering a limit stateof transfornultion of the structure into a mechanism, it shall be verified that
a
mechanism does not occur unless actioris exceed their design values, taking account ·of the respective design 'values of all structural properties. . .ETHIOPIAN BUILDING CODE STANDARD FOR DESIGN OF COMPOSITE STEEL AND CONCRETE STRUCTURES
/
(4) When considering a limit state of stability induced by second-order effects, it shall be verified that instability does not occur unless actions exceed their design values, taking account of the respective design values of all structural properties. In addition, sections shall be verified according to (2) above.
(5) When considering a limit state of rupture induced by fatigue, it shall be verified that the design value of the damage indicator Dd does not exceed unity, see Chapter 8. .
(6) When considering effects of actions, it shall be verified that:
Ed S;
c,
(2.9)where Ed is the design value of the particular effect of actions being considered
Cd is the design capacity for the effect of actions.
2.8.2.2 Combinations of Actions
(1) For each load case, design values Ed for the effects of actions shall be determined from combination rules involving the design values of actions given in Table 2.1.
Table 2.1 Design Values of Actions for use in the Combination of Actions
Design situation Permanent actions Gd Variable actions
o,
Accidental actions Ad Leading variable action Accompanying variable actions Persistent and transientAccidental
(if not specified differ ently else where)
'Yo
o,
'YOAo,
'YQa.
1/;]a.
1/;0 'YQ Qk 1/;2a.
'Y'YA Ak (if Adis not specified directly)
(2) The design value given in Table 2.1 shall be combined using the following rules (given in symbolic form):
(a) Persistent and transient design situations for verifications other than those relating to fatigue (fundamental combinations):
L'Yo,j Gk,j
+
'Yq,' Qk"+
L'YQ,i 1/;o,i Qk,i (2.10)(b) Accidental design situations (if not specified differently else where):
L 'YOA,j Gk,j
+
Ad+
1/;],] Qk,]+
L 1/;2,i Qk,i (2.11)where
«,
,] are the characteristic values of the permanent actionsQk,] is the characteristic value of one of the variable actions
a;
are the characteristic values of the other variable actions Ad is the design value (specified value} of the accidental actions'Yo.j is the partial safety factor for the permanent action Gk.j 'YOA.j is as 'YO.j but for accidental design situations
'YQ.i .is the partial safety factor for the variable action QK.i
1/;0' 1/;" 1/;2 are factors defined in Section 2.4.4.
CHAPTER 2: BASIS OF DESIGN
~3)
Combinations for accidental design situations either involve an explicit accidental action
Aor refer
to a situation after-an accidental event
(A :!:::0). Unless specified otherwise,
"YGA=
1.0 may be used
(4)IIi· Eqs.
(2.10) and (2.11),indirect actions shall be introduced where relevant.
(5) Simplified combinations for building structures are given in Section 2.
.8.3.1.2.8.2.3 Design Values of Permanent Actions
(1)
In the various combinations defined above, those permanent actions that increase the effect of the
variable actions (i.e. produce unfavourable effects) shall be represented by their upper design values
and those that decrease the effect of the variable actions
(i.e,produce favourable effects) by their
lower design values (see Section 2.4.6(2».
./
(2) Where the results of a verification may be very sensitive to variations of the magnitude of a single
permanent action from place to place in the structure, this action shall be treated as consisting of
separate unfavourable and favourable parts. This applies in particular to the verification of static
equilibrium, (see Section 2.8.2.4) ..
(3) Where a single permanent action is treated as consisting of separate unfavourable and favourable
,parts, allowance may be made for the relationship between these parts by adopting special design
Values (see Section 2.8.3.1(3) for' building structures).'
.
.
(4) Except for the cases mentioned in (2), the whole of each permanent action should be represented
throtighout the structure
by
either its lower or its upper design value, whichever. gives the more
.unfavourable effect.
'
(5) For continuous beams and frames, the same design value of the self-weight of the structure
. (evaluated as in Section 2.4.3(4)
may be applied to all spans, except for cases involving the static
equilibrium of cantilevers (see Section 2.8.2.4).
2.8.2.4· Verification of Static Equilibrium
(1) For the verification of static equilibrium, destabilizing (unfavourable) actions shall be represented
by upper design values and stabilizing (favourable) actions by lower design values (see Section
2.8.2.1(1»~(2) For stabilizing effects, only those actions which can reliably be assumed to be present in the
situation considered shall be included in the relevant combination.
.(3) Variable actions should be applied where they increase the destabilizing effects but omitted where
they would increase the stabilizing effects.
.
(4) Account should be taken of the possibility that non-structural elements might be omitted or
removed.
(5)' Permanent actions shall
berepresented by appropriate design values, depending on whether the
destabilizing and stabilizing'effects result from:
'
.
~a) 't~eunfavourable and th~
favourable parts of a single permanent action, see (9) below"and/or
(b),
different permanent actions, see
(10) below..
.
-,
ETHIOPIAN BUILDING CODE STANDARD FOR DESIGN OF COMPOSITE STEEL AND CONCRETE STRUCTURES
(6) The self-weights of any unrelated structural or non-structural elements made of different
construction materials should be treated as different permanent actions.
(7) The self-weight of a homogeneous structure should be treated as a single permanent action
consisting of separate unfavourable and favourable parts.
(8) The self-weights of 'essentially similar parts of a structure (or, of essentially uniform non-structural
elements) may also be treated as separate unfavourable and favourable parts of a single permanent
action.
(9) For building structures, the special partial safety factors given in Section 2.8.3.1(3) apply to the
unfavourable and the favourable parts of. each single permanent action, as envisaged in Section
2.8.2.3(2).(10) For building structures, the normal partial safety factors given in Section 2.8.3.1(1)
apply to
permanent actions other than those covered by
(9)above.
'
(11) For closely bounded or closely controlled permanent actions, smaller ratios of partial safety
factors may apply in the other parts'of EBCS 3.
.
(12)
Where uncertainty of the value of a geometrical dimension significantly affects the verification
.of static equilibrium, this dimension shall be represented in this verification by the most unfavourable
value that it is reasonably possible for it to reach.
2.8.3 Partial Safety Factors for tntimate
LimitStates
2.8.3.1 Partial Safety Factors lor Actions on Building 'Structures
(1) For the persistent and transient design siruations the partial safety factors' given in Table 2.2 shall
~u~. .
Table 2.2 Partial Safety Factors for Actions on Building Structures
for Persistent and Transient Design Situations.
Permanent
actions
('Yo)Variable actions
('YQ)Leading variable
actions
Accompanying
variable actions
Favourable effect
'YF,I/f 'Unfavourable
effect
'YF,sup 1,0'"1,30'"
p1.60
-1.60
'" See also Section 2.8.3,1(3)
(2) For accidental design situations 'to which Eq.(2.l0) applies, the partial safety factors for the
variable actions are taken as equal to 1.0.
C.HAPTER 2: BASIS QF DESIGN
(3) Where, according tOl 2.8.2.3(2), a single permanent action needs to be considered as. consisting
of unfavourable and favourable parts, the favourable part may, as an alternative, be multiplied by:
'YG.lnt
=
1.1 (2.12)and the unfavourable part by:
'YG.3up = 1.30 (2.13)
provided that applying "YG,II'/ = 1;{) both to the favourable part and to the unfavourable part does not
give·Plpre unfavourable effect.
.. _ ....
",.
(4) where the components of a vectorial effect can vary independently, favourable components (e.g. the.longitudinal force)' should be multiplied by a reduction factor:. . .
(5) For building structures, as a simplification, Eq.(2.1O) may be replaced by whichever of the following combinations gives the larger value:
(a) considering only the most unfavourable variable action:
L
'YG,} Gk,}+
'YQ,I Qk,I (2.14)(b) considering all unfavourable variable actions:
L
'YG,} GkJ+
0.9L
'YQ,I Qk,; (2.15)2.8.3.2 Partial Safety Factors for Resistances
(1) Partial safety factors for resistances are given in the relevant clauses in Chapters 4 and 6.
(2) For fatigue verifications see Chapter 8 of EBCS 2.
2.8.4 Serviceability Limit States
(1) It shall be verified that:
Ed ~ Cd or Ed ::;;.Rd (2.16)
Where Cd is a nominal value or a function of certain design properties of materials related to the design effect of actions considered, and
Ed is the design effect of actions, determined on he basis of one of the combinations defined below.
The required combination is identified in the particular clause for each serviceability verification, see Section 5.2.1(4) and Section 5,3,1(4),
(2) Three combinations of actions for serviceability limit states are defined by the following expressions:
Rare combination:
L
GkJ • Qk,]+ L
!/to,] Qk,] (2.17)
---_._---~----ETHIOPIAN BUILDING CODE STANDARD FOR DESION OF COMPOSITE STEEL AND CONCRETE STRUCTURES .
1:
frequent combination:
L GkJ
+
1/11,1 QklI+
L 1/12,1 Qk,1(2.18) ,
Quasi-permanent combination:
L GkJ+
L 1/12,1 Qk,l(2.19)
where the notation is defined in Section 2.8.2.2(2)
, I
(3)
Where simplified oompliance rules are given in the relevant clauses dealing with serviceability
limit states, detailed calculations using combinations of actions are not required.
(4)
Where the design considers compliance of serviceability limit states by detailed calculations,
simplified expressions may
beused for building structures.
(5)
For building structures,
as
a &bnplification, Eq. (2.17) for the rare combination may be replaced
, by whichever of the following combinations gives the larger value:'
(a) Considering only the most unfavourable variable action:
LGk,j
+
Qk,I(2.20)
(Q)
Considering all unfavourdble variable actions:
L GkJ
+
0.9
L Qk,1(2.21)
These two expressions may, also be 'used as a substitute for Eq.(2.18) for the frequent
combination.
(6) Values of
'YMshallbe taken as 1.0 for all serviceability limit states, except where stated otherwise
in particular clauses.
2.9DURABILITY
(1) To ensure an adequately durable structure, the following inter-related factors shall be considered:
I
(a) Use of the structure
(b) Required'performance criteria
-,(c) Expected environmental conditions
(d) Composition, properties and performance of the materials
(e) Shape of members and the structural detailing
(t)
Quality of workmanship and level of control
(g) Particular protective measures
.,.
"
(h) Likely maintenance during the intended life.
(2) The internal and external environmental conditions shallbe estimated at the design stage to assess
theirsignificance in relation to durability and to enable adequate provisions to be made for protection
of the materials.
/
-CHAPTER
3
MATERIALS
.3.1
CONCRETE
3.1.1 General
(1) The strength and other data for the concrete are defined on the basis of standard tests,
3.1.2 Grades of Concrete
(1) Concrete is graded in terms of its characteristic compressive cube strength. The grade of concrete
to be used in design 'depends on the classification of the concrete works and its intended use,
(2) Table 2.1 gives the permissible grades of concrete for the two classes of concrete works.
(3) The numbers in the grade designation denote the specified characteristic compressive strength in
MPa.
Table 3.1 Grades of Concrete
Class
Permissible Grades of Concrete
I
CS
C1S
C20
C25
C30
C40
C50
C60
II
CS
C1S
C20
Grade
CS shall be used only as lean concrete
3.1.3 Charac:tenstic Compressive Strength of Concrete
(1) For the purpose of this Code, compressive strength of concrete is determined from tests on
1S0mm cubes at the age of 28 days in accordance with standards issued or approved by Ethiopian
Standards.
(2) The characteristic compressive strength is defined as thatstrength below which 5%of all possible
strength measurements maybe expected to fall.
In practice, the concrete may be regarded as
complying, withthe grade specified for the design if the results of the tests comply withthe acceptance
criteria laid down in 'Chapter 9 of BBCS 3.
(3) Cylindrical' or cubical specimens of other sizes may also be, used with conversion factors
determined from a comprehensive series of tests. In the absence of such tests, the conversion factors
. given in Table 3.2.may, be applied to obtain the equivalent characteristic strength on the basis of
·150mm cubes. '
(4)In Table 3.3 the characteristic cylinder compressive strengthfck are given for the different grades
of concrete.
. '
EBCS 4 - 199519